On the planet Peladon, there is tension between the trisilicate miners and the ruling class. Gebeck (Rex Robinson) is the head miner and the hot-headed Ettis (Ralph Watson) is pushing him toward revolution. Queen Thalira (Nina Thomas), the somewhat overwhelmed daughter of the late King Peladon, has sympathy for the miners, but is keenly aware that her planet is vital to the war effort of the Galactic Confederation. The Vision of Aggredor (Nick Hobbs), the ancient Royal Beast, which has killed miners, has everyone frightened. Chancellor Ortron (Frank Gatliff) tells the Queen that this is a sign of displeasure at all the alien entanglements.
Into this, the TARDIS lands. The Doctor came to Peladon fifty years ago with companion Jo Grant and helped the young King Peladon deal with a conspiracy involving the Galactic Federation of the time. The Doctor is happy to see Alpha Centauri (voice of Ysanne Churchman and body of Stuart Fell), and the friendly barely humanoid alien is still the Federation Ambassador. The Queen has heard of the Doctor from her father the King and asks for his help. He guesses the otherworldly appearances of the monstrous Aggredor are all about trying to interrupt trisilicate production. There is a strike, Ettis leads an attack on the armoury, and the striking miners are armed. Human Engineer Eckersley (Donald Gee) talks Alpha Centauri into sending for Federation troops.
Both the miners and the rulers are unhappy with this, particularly when Commander Azaxyr (Alan Bennion) of the Ice-Warriors begins shooting people. All he cares about is trisilicate production. Otron and Gebek join forces against the Ice-Warriors, Ettis is killed trying to bomb the Citadel, the Ice-Warriors impose Martial Law, imprison the Queen, and kill Otron.
The fact is: Azaxyr and Eckersley are agents of the evil Galaxy Five and have arranged all this to control the trisilicate supply. The Vision of Aggredor—the Monster of Peladon—was created to cause panic. Gebek leads an assault on the Ice-Warriors. Azaxyr and his warriors are killed, as is Eckersley himself, at the hands of the misunderstood Aggredor, who is protecting the Queen. Galaxy Five capitulates, Queen Thalira tries to patch everything up with Gebek as her new Chancellor, and the Doctor slips away in the Tardis with Sarah Jane Smith.
The name trisilicate came from a toothpaste tube. The story did not get much love. The Ice-Warriors as bad guys were praised, but they did not appear on screen again until 39 years later. The story was inspired, obviously, by the 1973 U.K. miners’ strike. The rest of it came from The Curse of Peladon. The Doctor apparently dies and comes back to life again, and this inspires Elizabeth Sladen, but not the viewers overmuch. To be fair, Sladen was new to the companion role and just getting her sea-legs. She did a creditable job, as did many of the actors. One of the great gifts the BBC gave to Doctor Who was its range of guest-role talent. The miners were tough and brawling and brave despite their unfortunate badger-like hairdos. The human bad guy was really quite reasonable until it became time to reveal the depths of his evil. And the team who made Alpha Centauri did an impressive job of creating a likeable character inside all that foam and felt.